The electrostatic potential inside a charged spherical ball is given by : $V = b -ar^2$, where  $r$ is the distance from the centre ; $a$ and $b$ are constants. Then, the charge density inside the ball is :

  • A

    $24\pi \,a{\varepsilon _0}r$

  • B

    $6\,a{\varepsilon _0}r$

  • C

    $24\pi \,a{\varepsilon _0}$

  • D

    $6\,a{\varepsilon _0}$

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